1. Field of the Invention
The invention relates generally to a mixer and process directed to the utilization of crumb rubber produced from scrap tire carcass by effectively drying and converting crumb rubber to a Dry Liquid Concentrate enhancing the use of crumb rubber with asphalt, thermo plastic and chemically catalyzed materials where limited moisture is desired.
2. Description of the Prior Art
Each year there are an estimated 250,000,000 scrap tires discarded throughout the United States. Unwanted scrap tire piles, scattered throughout the country, have been estimated as high as 3 billion units. The poor biodegradability of scrap tire, their tendency to trap gases and rise to the surface in landfills, the serious fire hazard scrap tire piles represent, and the breeding environment that unwanted scrap tire piles offer to disease carrying pests, such as rodents and mosquitos, has caused them to be classified as a serious environmental nuisance.
Attempts to reuse the materials composing scrap tires have had very limited economic success. Many of these involve destructive distillation. The approaches to reuse, burn, or distill scrap tires appear not to have been commercially successful and had little effect on reducing either the flow or accumulation of scrap tire carcasses.
Truck tire carcasses with acceptable sidewall structure are recapped. The original tread stock of a used truck tire is removed by buffing. The resulting tire buffings, generated from the removal of the original tread stock, have been the primary feedstock material for the United States tire generated crumb rubber industry. This utilization, however, is limited in its scope and does not address the problem presented by scrap passenger or truck tire carcasses no longer suitable to be recapped.
Other methods of using scrap tire carcasses have included burning tire chips for BTU value and low and high vacuum pyrolysis to recover oil, carbon black, steel and fiber.
Several methods have been employed to enhance the value of scrap tire derived crumb rubber in vulcanized curing procedures. These methods are: polymeric coatings to enchanced-manufacture in rubber goods, addition of various quantities of tall oil derived fatty acids to adhere rubber particles into a useful mass, sulfur additions to act as a vulcanizing agent, and various complete devulcanization processes. The generated crumb rubber is also used in minimal percentages with virgin rubber as a filler and mixed with hot asphalt as a modifier.
Plastics is a multibillion dollar industry which produces synthetic materials and products, many of which were never dreamed of only a few years ago. Today, civilization requires synthetic materials (artificial resins produced by chemical reactions of organic substances). Many products made of plastic produced materials are produced at less cost than was possible with natural materials.
Plastics, unlike glass or aluminum, are not easily recycled back into useful products, such as those from which they were generated. Plastics, being a specifically engineered, rather than a generic material, are sorted prior to recycling. Plastics are seldom remanufactured back into the product or part which generated them. Often, recycled plastics are more expensive than new polymers. Examples of plastics which are recycled include (1) high-density polyethylene ("HDPE") and low-density polyethylene ("LDPE") into boards, binds, and trash cans and (2) polyethylene terephthalate ("PET") into carpet fiber. The markets for recycled plastics have been slow to develop and do not appear to be able to keep pace with the generation of new plastic materials. Once plastics are molded or spun, they lose some of the characteristics or properties of the virgin material. This creates a much bigger problem than scrap tires because the United States generates over 12 billion tons of scrap plastics per year, most of which is destined for deposit in landfills.
Moisture content can be a hindrance to the utilization of crumb rubber in heat driven applications. See U.S. Pat. Nos. 5,488,080 and 5,604,277, both of which are to John D. Osborn. Three common apparatus and methods of drying known in the prior art are illustrated below, when they were used to dry crumb rubber combined with tall oil and other fatty acids:
Compared Methods of Drying
1. The tray of a dehydration unit typical to drying foods such fruit was loaded with 1/2 pound of 30 mesh crumb rubber which had been combined with tall oil, fatty acid and residues of tall oil production at a by weight ratio of 10%. A Carl Fisher moisture test was performed on the mixture yielding a pre-dried moisture content of 0.79%. The unit was operated under standard low heat for a period of eight hours. After discharge, the temperature was measured at 180.degree. F. The Dry Liquid Concentrate was again tested for moisture by Carl Fisher. The resulting moisture content was measured at 0.34%. PA0 2. A fluidized bed dryer was heated to a temperature of 200.degree. F. A sample of 30 mesh crumb rubber was combined with tall oil, fatty acid at 10% by weight. A Carl Fisher moisture test was performed on the mixture yielding a pre-dried moisture of 0.87%. The Dry Liquid Concentrate was placed in the dryer and held for four hours. At discharge, the temperature of the Dry Liquid Concentrate was measured at 195.degree. F. A Carl Fisher moisture test was again performed yielding moisture content of 0.21%. PA0 3. A 300-liter horizontal mixer equipped with a vacuum pump and heated jacket was heated to 300.degree. F. A 100 pound sample of 30 mesh crumb rubber was combined with tall oil, fatty acids and residues of tall oil production at 10% by weight rate. A Carl Fisher moisture test was performed prior to drying yielding a result of 0.79%. A 15 minute cycle was performed with vacuum pulled to a total of 26.4 inches hg. Temperature at discharge was measured at 211.degree. F. A Carl Fisher moisture test was again performed yielding moisture content of 0.14%.
Crumb rubber or cross-linked granular rubber powder is hygroscopic by nature with a latent moisture content of typically less than one percent when produced by industry standard crumb rubber production technology. This moisture content interferes with crumb rubber's use in many heat driven applications such as molding with thermoplastics and blending with asphalt binder whose applications use heat in excess of 212.degree. F. Chemically catalyzed applications may also require crumb rubber to have limited moisture contents to optimize performance. Heat aging of the crumb rubber may also cause further vulcanization or crystallization of the rubber polymers limiting the effectiveness of direct heat as a drying method. Crumb rubber is a poor conductor of heat requiring excessive energy to drive off moisture. Excessive heat may also heat age the crumb rubber limiting usefulness.
It would be desirable to develop a cost feasible economic method of processing crumb rubber into a substantially dry raw material for use in heat driven applications such as thermoplastic, asphalt binder modification, as well as moisture-sensitive chemically-catalyzed materials.
It is well-known in the art to use tall oil with ground rubber waste for reuse as rubber. See "Ground Rubber Waste--A Supplementary Raw Material for the Rubber Industry" issued by Kahl & Co.; U.S. Pat. No. 4,481,335, issued Nov. 6, 1984 to Stark, Jr. entitled "Rubber Composition and Method"; U.S. Pat. No. 3,873,482, issued Mar. 25, 1975 to Severson et al., entitled "Pyrolyzed Tall Oil Products as Synthetic Rubber Tackifiers"; U.S. Pat. No. 4,895,911, issued Jan. 23, 1990 to Mowdood et al., entitled "Tall Oil Fatty Acid Mixture in Rubber"; U.S. Pat. No. 4,792,589, issued Dec. 20, 1988 to Colvin et al., entitled "Rubber Vulcanization Agents of Sulfur and Olefin"; and U.S. Pat. No. 4,224,841, issued Jan. 13, 1981 to Frankland, entitled "Method for Recycling Rubber and Recycled Rubber Product". Generally for the area of ground polymer elastomer operation, see US. Pat. No. 4,771,110, issued Sep. 13, 1988 to Bouman et al., entitled "Polymeric Materials Having Controlled Physical Properties and Purposes for Obtaining These"; and for rubber discussions see U.S. Pat. No. 3,544,492, issued Dec. 1, 1970 to Taylor et al., entitled "Sulfur Containing Curing Agents"; and "Organic Chemistry" by Fieser and Fieser printed 1944 by D. C. Heath & Co. Boston, pages 346 and 347.